Beetroot Juice Does Not Enhance Supramaximal Intermittent Exercise Performance in Elite Endurance Athletes.

Objective: Nitrate (NO3-)-rich beetroot juice (BR) is recognized as an ergogenic supplement that improves exercise tolerance during submaximal to maximal intensity exercise in recreational and competitive athletes. A recent study has investigated the effectiveness of BR on exercise performance during supramaximal intensity intermittent exercise (SIE) in Olympic-level track cyclists, but studies conducted in elite endurance athletes are scarce. The present study aimed to determine whether BR supplementation enhances the tolerance to SIE in elite endurance athletes.Methods: Eleven elite endurance athletes (age: 21.7 ± 3.7 years, maximal oxygen uptake [Formula: see text] 71.1 ± 5.2 mL·kg-1·min-1) performed an SIE test until exhaustion following either a 3-day BR supplementation (340 mg/d) or a placebo (PL) supplementation (<2.5 mg/d) in a randomized, single blind, placebo-controlled, and crossover study. The exercise test consisted of 15-second cycling exercise bouts at 170% of the maximal aerobic power interspersed with 30-second passive recovery periods. Gas exchange was measured during SIE tests as local muscle O2 delivery and extraction were assessed by near infrared spectroscopy.Results: The number of repetitions completed was not significantly different between BR (13.9 ± 4.0 reps) and PL conditions (14.2 ± 4.5 reps). BR supplementation did not affect oxygen uptake ([Formula: see text]) during SIE tests (BR: 3378.5 ± 681.8 mL·min-1, PL: 3466.1 ± 505.3 mL·min-1). No significant change in the areas under curves was found for local muscle total hemoglobin (BR: 6816.9 ± 1463.1 arbitrary units (a.u.), PL: 6771.5 ± 3004.5 a.u.) and deoxygenated hemoglobin (BR: 6619.7 ± 875.8 a.u., PL: 6332.7 ± 1336.8 a.u.) during time-matched work + recovery periods from SIE tests following BR supplementation.Conclusions: BR supplementation does not enhance the tolerance to SIE in elite endurance athletes and affects neither [Formula: see text] nor local muscle O2 delivery and extraction.

Plasma asymmetric dimethylarginine concentrations are not related to differences in maximal oxygen uptake in endurance trained and untrained men.

NEW FINDINGS: What is the central question of this study? Is there an association of plasma concentration of asymmetric dimethylarginine, which is related to exercise capacity in patients with cardiovascular diseases, with oxygen delivery and subsequently exercise capacity in healthy subjects in the absence of the potentially confounding influence of inflammation and oxidative stress? What is the main finding and its importance? Plasma asymmetric dimethylarginine concentrations are not related to exercise capacity in healthy subjects, while O2 delivery in the working skeletal muscle during the maximal graded-exercise test is not associated with any of the l-arginine analogues. ADMA alone does not play a crucial role in local muscle perfusion and in maintaining exercise capacity. ABSTRACT: Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthesis that could limit oxygen (O2 ) delivery in the working skeletal muscles by altering endothelium-dependent vasodilatation. Exercise capacity is associated with plasma ADMA concentrations in patients with cardiovascular diseases, but this issue has still not been investigated in healthy subjects. We aimed to determine whether plasma ADMA concentrations were negatively associated with exercise capacity in young healthy male subjects. Ten men with maximal oxygen uptake ( V ̇ O 2 max ) > 65 mL kg-1  min-1 were included in the high exercise capacity group (HI-FIT), and 10 men with V ̇ O 2 max  < 45 mL kg-1  min-1 were included in the low exercise capacity group (LO-FIT). Plasma ADMA and other l-arginine analogue concentrations were measured before and after a maximal graded-exercise test by liquid chromatography-tandem mass spectrometry. Microvascular O2 delivery during exercise was estimated through the pattern from the sigmoid model of muscle deoxygenation in the vastus lateralis measured by near infrared spectroscopy. V ̇ O 2 max was 60% higher in the HI-FIT group (median: 70.2 mL kg-1  min-1 ; IQR: 68.0-71.9 mL kg-1  min-1 ) than in the LO-FIT group (median: 43.8 mL kg-1  min-1 ; IQR: 34.8-45.3 mL kg-1  min-1 ). Plasma ADMA concentrations did not differ between the LO-FIT and HI-FIT groups before (0.50 ± 0.06 vs. 0.54 ± 0.07 µmol L-1 , respectively) and after the maximal incremental exercise test (0.49 ± 0.08 vs. 0.55 ± 0.03 µmol L-1 , respectively). There was no significant association of plasma ADMA concentrations with the pattern of local muscle deoxygenation and exercise capacity. Exercise capacity and microvascular O2 delivery are not related to plasma ADMA concentrations in young healthy male subjects. Our findings show that ADMA does not play a crucial role in local muscle perfusion and in maintaining exercise capacity without pathological conditions.